This invention relates to dynamic seal assemblies of the type including air flow past the seal to prevent oil or contaminants from moving in a direction opposite to such air flow. In particular, this invention relates to an improved dynamic seal which includes a bellows-like tube of resilient material enabling movement of the seal in a radially outward direction and being radially and axially stabilized by air jets in these directions.
Internal combustion engines require efficient seals at the ends of the crankshaft. These sealing means in the form of circumscribing seals perform several functions. First, they retain oil or other lubricant in the engine's crankcase. Second, they prevent contaminants from entering the engine from the surrounding environment. Such contaminants can, of course, result in shortened engine life.
One type of seal that has been found to be effective in this environment is that shown in U.S. Pat. No. 3,575,426 assigned to the assignee hereof. With this patent device a pair of lip seal assemblies are coaxially mounted around a rotational shaft to form a chamber therebetween adapted to be pressurized by air which lifts the seal out of contact with the shaft. In this manner, continuous streams of air will flow past the seals to prevent oil or contaminants from moving in a direction opposite to such air flow. In addition, seal life is enhanced because the seals do not normally run against the surface of the shaft. When the shaft is at rest, inherent resiliency of the seals or retainer springs located radially outwardly of the lips normally effects a positive contact with the shaft to contain oil or exclude contaminants. However, the subject seal tends to be rather stiff and lacks the flexibility desired. This results in some control problems being engendered in the selection of the amount of air flow necessary to lift the lip from the shaft surface.
Another problem is engendered by the slight but rapid wobble that is encountered with the shaft, such as a crankshaft, about which the seal is placed. This wobble increases as shaft rotational speed increases and tends to break down the sealing effect of normal seals.